In recent years, in accordance with, for example, a demand for reducing travel cost and time, a communication system which provides calling and conferencing over a communication network such as the Internet or a dedicated line or the like has become popular. In this kind of communication system, when a communication between communication terminals is started, content data such as image data and audio data are sent and received, and a video-conference, a phone call, or the like can be realized.
Further, in such a communication system used for video-conferences, multiple destinations can be registered so that a user can select one of these destinations to start a conference with a desired partner (see PTL 1).
Further, a method has been known in which a communication terminal makes a request for starting communication with a call center, to a management system (see PTL 2). The management system calls a destination communication terminal among communication terminals at the call center, and establishes a session between the communication terminal being the source of the start request, and the communication terminal being the destination.